Who fucked up the most in human history?

He was an ambitious scientist who had the idea to put lead in fuel before we knew how bad it was. Then he created CFCs for refrigerators that we later learned are responsible for eating through the ozone layer.

He has accidentally achieved the highest environmental damage of any one organism.

Then, when he was old an bed ridden, he designed a contraption to make walking and standing etc easier. His contraption failed and killed him.

You really shouldn't he was an asshole. He knew about the detrimental effects of lead fuel and knew personally about the effects of lead poisoning and how it induced mania into the people who would work with lead products, but was too proud to admit it and stood by lead petroleum until his death.

Industrial applications still install and use ammonia as a refrigerant to this day. You'll use significantly larger quantities of ammonia than you would R-410a or another modern working fluid, but you can buy ammonia by the tank-car full.

It's not used in residential applications because leaks would be hazardous, but industrial users are willing to monitor for them in exchange for the cost savings.

They use ammonia in the radiators of the space station. Because an ammonia leak in the cabin would be disastrous, it can only be used outside. There are heat exchangers and water is used to move heat in the cabin. External equipment, most prominently the solar panels, are directly cooled off of dedicated ammonia loops. If astronauts have to perform maintenance on one of the external cooling systems, there are special procedures to decontaminate the space suits before being allowed to come back inside. (Exposing the suits to the unfiltered rays of the sun for 10 or so minutes will bake any spilt ammonia off.)